1. Field of the Invention
This invention relates to the inspection of containers and, more particularly, to apparatus and methods for inspecting such containers for finish dimensions and finish defects or irregularities.
2. Brief Description of the Prior Art
Inspecting containers to ensure that finish dimensions fall within acceptable tolerances and to detect surface defects is important in modern container manufacturing, processing and filling operations. For example, finish defects and containers of improper size can damage on-line production machines, cause of loss of product and result in unusable, or even dangerous, containers.
Some finish defects that typically occur in blown plastic bottles include blown finish defects, skirt defects, and improper dimensions. Blown finish defects often occur when the finish of the container overhears in the blow molding process and the container finish splits or otherwise deforms during the application of pressure to expand the container preform into the mold. Skirt defects may include non-parallel sides of the safety ring groove that result in such groove being of incorrect depth. Improper dimensions can result in non-capable containers and/or can permit removal of the safety or locking ring of the closure from the container without removal of the cap.
Containers may be manually inspected for finish defects and proper finish dimensions. Manual inspection has several disadvantages. It is extremely difficult to detect or remove containers with oversized dimensions from container production lines using manual inspection. In addition, modern production lines, such as container manufacturing and filling operations, typically operate at very high speeds. For example, such lines may operate at speeds on the order of 25,000 containers per hour or higher. Manual inspection of containers moving at such speeds is difficult.
Many types of automated apparatus for inspecting containers are known. For example, U.S. Pat. Nos. 2,937,749; 2,988,218; 3,782,542; 3,249,223; and 3,815,248 disclose apparatus for inspecting various exterior dimensions of containers.
In addition, U.S. Pat. Nos. 3,273,710 and 3,196,550 disclose apparatus for inspecting containers for the presence of surface irregularities and to detect whether the containers are of proper height.
U.S. Pat. No. 4,433,785 discloses an apparatus for determining whether the bottom of the container is perpendicular to the vertical axis of the container. It has also been known to rotate the container being inspected about its vertical axis during inspection thereof. Such rotation enables the entire circumference of the container at the level of inspection to be inspected.
It has also been known to inspect the thickness of containers using multiple sensors so that more than one container can be inspected simultaneously. U.S. Pat. No. 5,097,216 discloses a method and apparatus for inspecting the thickness of more than one container simultaneously using multiple sensors.
Despite the prior art, there remains a need for an apparatus and method for inspecting the finish of containers which provide simple and more reliable measurement of the finish dimensions of and detection of finish defects or irregularities on containers while such containers are moving sequentially at relatively high speeds. In addition, there remains a need for apparatus and method of inspecting containers which can simultaneously inspect more than one container at more than one location or level.